Well, I recommend using simple decks like Montana and Rescue. They can seem weak but they are so effective.
But the point of Elo is not a good deck. A useful deck is important of course, but the true deck is the deck that you already know the tactics. Elo is about patience. If you can play the game good and if you are patient, 1400 is possible with almost any deck. You can simply use the clan you know best

The obvious answer is that it all depends on the weekly meta. After getting a good weekly build know the matchups and what to do in almost every scenario.

Now if you are looking for one clan to use week in and week out its all preference. Like personally I use a half deck(2 of the 3) with either montana, piranahs, jungo. I also have a mono variant for montana and piranahs. I feel having a combination of clans will allow you to be ready every week.

So find a clan or two that fits your style and adjust to the weekly meta.